1. Field of the Invention
This invention broadly relates to appliances that are used during the course of orthodontic treatment. More particularly, the present invention relates to an orthodontic appliance that is affixed to one of the patient's molar teeth.
2. Description of the Related Art
Orthodontic therapy is a specialized type of treatment within the field of dentistry, and involves movement of malpositioned teeth to orthodontically correct locations. Orthodontic treatment often improves the patient's occlusion and typically enhances the aesthetic appearance of the teeth.
Many types of orthodontic treatment programs involve the use of a set of tiny appliances and wires that are commonly known collectively as “braces”. During such treatment programs, small appliances known as brackets are fixed to the patient's anterior, cuspid and bicuspid teeth, and an archwire is inserted into an archwire slot of each bracket. The archwire forms a track to guide movement of the teeth to orthodontically correct locations.
End sections of orthodontic archwires are typically captured in tiny appliances known as buccal tubes. Buccal tubes are affixed to the patient's molar teeth. In the past, buccal tubes were typically welded to bands having a configuration adapted to encircle the selected molar tooth. Recently, buccal tubes have become available that are adapted to be directly bonded to the surface of the patient's tooth by an adhesive.
Ligatures are often used in conjunction with orthodontic brackets to connect the archwire to the brackets and urge the archwire into an orientation of seating engagement in the archwire slot. One type of commercially available orthodontic ligature is a small, elastomeric O-ring. Orthodontic O-ring ligatures are installed by stretching the O-ring around small wings on the brackets that are known as tiewings. The tiewings are connected to the body of the bracket on its gingival side (i.e., the side facing the patient's gingiva or gums) and are also connected to the bracket body on its occlusal side (i.e., the side facing the outer tips of the patient's teeth). Once installed, the O-ring ligature extends around the back or lingual side of the tiewings as well as over the front or labial side of the archwire and urges the archwire toward a fully seated position in contact with a bottom or lingual wall of the archwire slot.
Metal ligatures, such as ligatures made of stainless steel, are also used to retain archwires in archwire slots of orthodontic brackets. Metal ligatures are typically made of a short section of initially straight wire that is subsequently formed into a loop. During installation, the wire ligature is hooked around the tiewings and extended over the labial side of the archwire. End sections of the archwire are then twisted together to close the loop and retain the ligature as well as the archwire in place.
Many types of orthodontic buccal tubes have an enclosed passageway for receiving the archwire, in contrast to the archwire slots of brackets that are open along one side. Some buccal tubes do not have tiewings since the enclosed passageway serves to capture the archwire. Buccal tubes are often of relatively simple construction, consisting essentially of a tubular body having a base that is adapted to be welded to an orthodontic band.
However, certain types of buccal tubes are known as “convertible” buccal tubes. These buccal tubes are often used on the first molar teeth of adolescent patients whose second molar teeth have not yet erupted. Convertible buccal tubes have an archwire passageway that is initially closed during the early stages of treatment. As treatment progresses and as the second molar tooth erupts, the passageway of the buccal tube on the first molar tooth is opened to convert the buccal tube into a bracket. Another buccal tube is then affixed to the patient's second molar teeth for capturing the ends of the archwire.
Examples of convertible buccal tube appliances are described in U.S. Pat. Nos. 4,511,331, 4,820,151, 4,927,362 and 5,059,119. Convertible buccal tubes often have a tab or cover that initially extends over and closes the archwire passageway. When it is desired to convert the buccal tube into a bracket, the tab or cover is opened to change the enclosed passageway into a slot that is open along one side. The practitioner then places a ligature around tiewings of the appliance and the archwire in order to retain the archwire in the archwire slot.
Unfortunately, some orthodontists are not entirely satisfied with elastomeric and metal ligatures used with orthodontic brackets and convertible buccal tubes. Such ligatures are somewhat time-consuming to install, both during initial installation and also during reinstallation whenever replacement of the archwire or ligatures is desired. As can be appreciated, decreasing the amount of time needed for ligation can help to reduce the total time that the practitioner must spend with the patient and consequently decrease the overall costs of orthodontic treatment.
Other disadvantages are also associated with elastomeric and metal ligatures. For example, there have been reports that certain polyurethane elastomeric ligatures have exhibited deformation and force decay during the course of treatment. In some instances, elastomeric ligatures are stained by food and beverages consumed by the patient and become somewhat unsightly. Metal ligatures often have sharp ends that may retain plaque and food debris and also may increase the risk of infection.
In an effort to overcome the problems associated with conventional ligatures, a variety of orthodontic brackets have been proposed in the past having various types of latches for coupling the archwire to the bracket. Such brackets are also known as self-ligating or tieless brackets. The latch comprises a movable clip, spring member, cover, shutter, bail or other structure that is connected to the bracket body for retaining an archwire in the archwire slot.
Examples of self-ligating orthodontic brackets having generally U-shaped ligating latch clips are described in U.S. Pat. Nos. 3,772,787, 4,248,588 and 4,492,573. In general, the clip of such brackets is slidably mounted on the bracket body, and a dental explorer or other small-tipped dental tool is used to move the clip relative to the body when needed in order to open or close the archwire slot. A self-ligating bracket known as the “Speed” brand bracket also has a movable, generally U-shaped clip for ligating the archwire to the bracket.
Other types of self-ligating brackets have latches that resemble swinging shutters or closures that pivotally move between a slot-open and a slot-closed position. For example, the bracket illustrated in U.S. Pat. No. 4,712,999 has a rotatable cover plate that is pivotally connected at one end to a tiewing of the bracket along one side of the slot, and is releasably engagable at the other end with a tiewing that is located along the opposite side of the archwire slot. Other orthodontic brackets with swinging latches are described in U.S. Pat. Nos. 4,103,423, 5,516,284 and 5,685,711.
U.S. Pat. Nos. 4,371,337 and 4,559,012 describe self-ligating orthodontic brackets having latches that rotate about the longitudinal axis of the archwire slot. The latch of these references has a somewhat cylindrical shape and is rotatably received in a mating, cylindrical channel, and an outwardly extending arm is provided to assist in rotatably moving the latch between a slot-open and a slot-closed position.
A self-ligating orthodontic bracket that is described in U.S. Pat. No. 5,711,666 has a latch that comprises a flexible flat spring member. One end of the spring member is fixed to the bracket body on one side of the archwire slot, and the opposite end of the spring member has notches that releasably engage latch sears or catches when the spring member is moved to a slot-closed position. To open the slot, the notches are disengaged from the catches and the spring member is bent to an orientation sufficient to enable the archwire to be removed from the archwire slot.
Other types of self-ligating orthodontic brackets have latches that comprise essentially flat plates that are slidable between a slot-open and a slot-closed position. Examples of such construction are shown in U.S. Pat. Nos. 5,094,614, 5,322,435 and 5,613,850. In general, the sliding latches described in those references move in upright channels that are located buccolabially of the archwire slot.
Another type of self-ligating bracket that has been proposed in the past has a latch that is made of a section of wire material that functions similar to a bail. The orthodontic brackets described in U.S. Pat. Nos. 4,149,314, 4,725,229 and 5,269,681 have wire-like latches that swing between a slot-closed position and a slot-open position. The orthodontic bracket described in U.S. Pat. No. 4,260,375 has a wire latch that is slidable between a slot-open and a slot-closed position.
Improved self-ligating orthodontic brackets are described in two pending PCT applications entitled “ORTHODONTIC APPLIANCE WITH SELF-RELEASING LATCH”, WO01/22901 and US02/09896. The appliances described in these applications have a latch for retaining an archwire in the archwire slot, and the latch releases the archwire from the archwire slot whenever the archwire exerts a force on the appliance that exceeds a certain minimum value. The minimum value is significantly less than the force required in the same direction to debond the appliance from the tooth, and consequently helps ensure that the appliance will not spontaneously debond from the tooth during the course of treatment.
In certain embodiments of the appliances described in the PCT applications mentioned above, the archwire may be inserted into the archwire slot by pressing the archwire against the latch. The latch is constructed to self-open without the need for hand instruments or other tools. Consequently, such appliances are a great advantage to the practitioner in that the time needed for connecting the archwire to the appliance can be significantly reduced.
The appliances described in the above-mentioned PCT applications include both brackets for the patient's anterior, cuspid and bicuspid teeth as well as appliances for the patient's molar teeth. While such appliances represent a significant advance in orthodontic appliance technology, there is a continuing need to improve the state of the art relating to self-ligating appliances. In particular, there is a need for an improved self-ligating appliance that is especially adapted for use with the patient's molar teeth. Preferably, any such appliance would provide a strong and secure coupling between the archwire and the associated molar tooth, and yet facilitate movement of the teeth when desired so that treatment can be completed without undue delay.